Calibration free distance sensor

ABSTRACT

One or more embodiments are directed to a magnet configured to be coupled to an object under test, an array of sensors configured to measure a magnetic field associated with the magnet, and a circuit configured to obtain voltage readings based on the measured magnetic field from the array of sensors and compute a distance between the array of sensors and the magnet based on the obtained voltage readings.

FIELD OF INVENTION

The present disclosure relates generally to sensors, and morespecifically, to calibration free magnetic distance sensors.

DESCRIPTION OF RELATED ART

Short range distance measurements (e.g., about 0.1 millimeters (mm) toabout 1 meter (m)) are often needed in many applications, such as inconnection with electronics and mechanical manufacturing, metrology,microscopy, lithography, and assembly line testing. Conventional sensorsmay require calibration to convert a signal to a distance. For example,an ultrasonic sensor may require calibration to account for the speed ofsound, which may vary as a function of temperature. A capacitive sensormay require calibration to account for a variation in its dielectricspacer and/or a fringing effect associated with the capacitor platearea.

BRIEF SUMMARY

According to one or more embodiments of the present disclosure, a systemfor providing a calibration free sensor comprises a magnet configured tobe coupled to an object under test, an array of sensors configured tomeasure a magnetic field associated with the magnet, and a circuitconfigured to obtain voltage readings based on the measured magneticfield from the array of sensors and compute a distance between the arrayof sensors and the magnet based on the obtained voltage readings.

According to one or more embodiments of the present disclosure, anapparatus comprises at least one processor, and memory havinginstructions stored thereon that, when executed by the at least oneprocessor, cause the apparatus to obtain at least one Hall voltagereading from each of a plurality of sensors associated with an array ofsensors, and compute a distance between a magnet coupled to an objectunder test and the array of sensors based at least in part on theobtained Hall voltage readings.

According to one or more embodiments of the present disclosure, anon-transitory computer program product comprises a computer readablestorage medium having computer readable program code stored thereonthat, when executed by a computer, performs a method comprising readinga voltage from each of a plurality of Hall sensors associated with anarray, fitting the read voltages as a function of position along a linebetween a magnet and the array, calculating a slope and an interceptassociated with the fit voltages, and calculating a distance between themagnet and the array based on the slope and intercept.

According to one or more embodiments of the present disclosure, a methodcomprises reading a voltage from each of a plurality of Hall sensorsassociated with an array, fitting the read voltages as a function ofposition along a line between a magnet and the array, calculating aslope and an intercept associated with the fit voltages, and calculatinga distance between the magnet and the array based on the slope andintercept.

Additional features and advantages are realized through the techniquesof the present disclosure. Other embodiments and aspects of thedisclosure are described in detail herein. For a better understanding ofthe disclosure with the advantages and the features, refer to thedescription and to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe disclosure are apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a graph illustrating an exemplary plot of a magnetic field asa function of position in accordance with one or more aspects of thisdisclosure.

FIG. 2 is a schematic block diagram illustrating an exemplarycalibration free sensor system in accordance with one or more aspects ofthis disclosure.

FIG. 3 is a flow diagram illustrating an exemplary method in accordancewith one or more aspects of this disclosure.

FIG. 4 is a graph illustrating an exemplary plot of a magnetic field orHall voltage as a function of distance in accordance with one or moreaspects of this disclosure.

DETAILED DESCRIPTION

It is noted that various connections are set forth between elements inthe following description and in the drawings (the contents of which areincluded in this disclosure by way of reference). It is noted that theseconnections in general and, unless specified otherwise, may be direct orindirect and that this specification is not intended to be limiting inthis respect. In this regard, a coupling of entities may refer to eithera direct or an indirect connection.

In some embodiments, a calibration free magnetic distance sensor mayinclude an array of sensors, such as Hall sensors. In some embodiments,a spherical magnet may be mounted on an object under test, and thespherical magnet may produce or generate a magnetic field in accordancewith a 1/d³ distance dependence or relationship. Analyzing the magneticfield measured by the array of sensors may yield a distance to themagnet, and hence, to the object under test. The measurement may beindependent of the magnet's magnetic moment or a conversion factorassociated with the sensor(s). Thus, a low-cost, calibration free,non-contact, and robust solution may be provided for measuring distance.

A magnet (e.g., a cylindrical magnet, a spherical magnet, or a magnet ofany other configuration or geometry) may be used as a source of amagnetic field. In some embodiments, the distribution of the magneticfield may adhere to that of an ideal point dipole magnet, following a1/d³ dependence along the dipole axis. The magnetic field of a pointdipole at any position vector r may be given by the following equation#1:

$\begin{matrix}{{B(r)} = {\frac{\mu_{0}}{4\pi}\frac{{3{\hat{r}\left( {\hat{r} \cdot m} \right)}} - m}{r^{3}}}} & {{Eq}.\mspace{14mu} {\# 1}}\end{matrix}$

In equation #1, B is the magnetic field vector, m is the magnetic momentvector, {circumflex over (r)} is the unit vector of r and μ₀ is themagnetic permeability in a vacuum.

Along a magnetic dipole axis z (see the inset of FIG. 1), equation #1may simplify to equation #2 as follows:

$\begin{matrix}{B_{z} = {\frac{\mu_{0}}{2\pi}\frac{m}{z^{3}}}} & {{Eq}.\mspace{14mu} {\# 2}}\end{matrix}$

In equation #2, m may be the magnetic moment of the magnet thatrepresents the strength of the magnet. This magnetic field can bemeasured by a Hall sensor to yield a voltage V_(H) proportional to themagnetic field, as described in equation #3:

V_(H)=kB_(z)   Eq. #3

In equation #3, k may correspond to a conversion factor.

In principle, by measuring the magnetic field B_(z) using a Hall sensor,the distance to the magnet could be determined. However, such adetermination might require measurement or “calibration” of the magneticmoment m (equation #2) and the conversion factor k (equation #3).Furthermore, for measurements performed over a long operation time, themagnetic moment m may vary. Such variation may be large, especially inan environment full of vibrations or characterized by high ambienttemperature.

Embodiments of the disclosure may eliminate a need to performcalibration. For example, assuming that a magnet is placed at an unknowndistance d from an initial position z′=0, equation #2 may be rewrittenas equation #4 as follows:

$\begin{matrix}{B_{z}^{{- 1}/3} = {\left( \frac{\mu_{0}m}{2\pi} \right)^{{- 1}/3}{\left( {z^{\prime} + d} \right).}}} & {{Eq}.\mspace{14mu} {\# 4}}\end{matrix}$

Using equation #3, equation #4 may be expressed in terms of Hall voltage(V_(H)) in equation #5 as follows:

$\begin{matrix}{V_{H}^{{- 1}/3} = {\left( \frac{k\; \mu_{0}m}{2\pi} \right)^{{- 1}/3}\left( {z^{\prime} + d} \right)}} & {{Eq}.\mspace{14mu} {\# 5}}\end{matrix}$

As expressed, equations #4 and #5 yield a linear relationship of theform y=a+bx between B_(z) ^(−1/3) (or V_(H) ^(−1/3)) and z′. Such alinear relationship is reflected in an example of experimental dataplotted in FIG. 1, where a Hall sensor 102 may be moved (e.g., movedcontinuously) from z′=0.

A linear fit may be performed with respect to the data associated withFIG. 1 to obtain the slope b and intercept a. Afterwards, the distance dmay be calculated in accordance with equation #6 as follows:

d=−a/b   Eq. #6

Using such a technique, it might not be necessary to know the magneticmoment or strength m or the conversion factor k to computer the distanced from the sensor 102 to a magnet 104. Thus, a calibration freetechnique may be provided.

In some embodiments, an array of sensors may be used to implement acalibration free distance sensor. The array of sensors may include twoor more sensors, such as two or more Hall sensors. The array of sensorsmay be arranged in accordance with one or more geometrical shapes orparameters. For example, in some embodiments a linear array may be used.

FIG. 2 is a schematic block diagram illustrating an exemplarycalibration free sensor system. A sensor assembly 202 may include anarray 204. The array 204 may include a number of sensors. For example,as shown in FIG. 2, the array 204 may include sensors 204-1, 204-2, and204-3. The sensors 204-1 and 204-2 may be separated by a distance d₀,and the sensors 204-2 and 204-3 may be separated by a distance d₁. Insome embodiments, the separations d₀ and d₁ may be the same (e.g.,d₀=d₁) and may be predetermined. In some embodiments, one or more of thesensors 204-1 through 204-3 may correspond to the sensor 102 of FIG. 1.

A magnet 206 (e.g., a spherical magnet), which may correspond to themagnet 104 of FIG. 1, may be mounted on an object under test 208, inorder to determine a distance d from the object 208 to the array 204.The magnet 206 and/or the object 208 may be placed in a line under thearray 204.

The array 204 may be configured to measure a magnetic field (B_(z))associated with the magnet 206. For example, a voltage from each of thesensors 204-1 through 204-3 may be provided to a voltmeter 210 via oneor more selection mechanisms, such as a multiplexer 212. The address orselect lines of the multiplexer may be provided by a controller 214.

In some embodiments, the controller 214 may include a processor 214 a,and a memory 214b storing instructions that, when executed by theprocessor 214 a, cause the controller 214 to perform one or more of themethodological acts as described herein. In some embodiments, the memory214 b may store data, such as measurements provided by the voltmeter210, address and/or select line values for the multiplexer 212,computations of the magnetic field B_(z) and/or distance d, etc.

In some embodiments, an aggregation device or circuit 220 may beconfigured to obtain and/or store the readings (e.g., voltage readings)from the sensors 204-1 through 204-3. That same device or circuit, oranother device or circuit (e.g., a computation device or circuit 222)may be configured to calculate the distance d based on the readings. Insome embodiments, the voltmeter 210, the multiplexer 212, and/or thecontroller 214 may be included in the aggregation device/circuit 220and/or the computation device/circuit 222. In some embodiments, one ormore of the entities of FIG. 2 may be included in one or more circuits.

FIG. 3 is a flow diagram illustrating an exemplary method. The methodmay be operative in connection with one or more architectures orsystems, such as those described herein. For ease of explanation andillustration, the method of FIG. 3 is described below in connection withthe system of FIG. 2. The method may be used to determine the distance dof the magnet 206 (and hence the object 208) from the array 204.

In block 302, the method may start or begin. As part of block 302, oneor more initialization processes or routines may be invoked. Forexample, a first sensor (e.g., the sensor 204-1) may initially beselected, and the controller 214 may provide corresponding address orselect line values to the multiplexer 212.

In block 304, the voltage from the selected sensor (generally denoted assensor ‘#i’ in FIG. 3) may be read by the voltmeter 210. The readvoltage, potentially in combination with the values for the address orselect lines of the multiplexer 212, may be saved at or stored by thecontroller 214, or another entity not necessarily shown in FIG. 2. Moregenerally, the read voltage may be saved in associated with indiciaindicative of the selection of a given sensor.

In block 306, a determination may be made whether voltages have beenread from all the sensors (e.g., all of the sensors 204-1 through204-3). If not (e.g., the “No” path is taken out of step 306), then theaddress or select lines of the multiplexer may be changed (e.g.,incremented) in block 308 to prepare to read the voltage from another orthe next sensor. If all the sensors have been read (e.g., the “Yes” pathis taken out of block 306), then flow may proceed to block 310.

In block 310, the controller 214 (or another entity) may linearly fitthe voltages read in connection with blocks as a function of positionalong z′. The fitting may be based at least in part on the predeterminedor known separation or spacing between the sensors 204-1 through 204-3included in the array 204. From the fit, characteristics such as slope(b) and intercept (a) may be calculated.

In block 312, the distance d may be calculated in accordance withequation #6 described above. The calculated distance d may be output to,e.g., an analog signal like voltage proportional to the distance, adigital signal containing an information of the distance, a displayscreen (e.g., a computer monitor), an email, a text message, a document,a fax/facsimile machine, a voice message, etc.

In block 314, the method may stop or end.

The blocks or events described above in connection with FIG. 3 areillustrative. In some embodiments, one or more events (or a portionthereof) may be optional. In some embodiments, one or more additionalevents not shown may be included. For example, in some embodiments avoltage may be read from a given sensor multiple times as part of afiltering or averaging algorithm to reduce the impact of non-idealities(e.g., noise) and/or to improve the accuracy or resolution. In someembodiments, the events may execute in an order or sequence differentfrom what is shown in FIG. 3.

FIG. 4 is a graph illustrating an exemplary plot of a magnetic field orhall voltage as a function of location or position. In some embodiments,the graph of FIG. 4 may be obtained having executed the method of FIG. 3in connection with the system of FIG. 2. The graph of FIG. 4 shows themagnetic field B_(z) or the Hall voltage V_(H) as a function of positionor location along the z-axis of FIG. 2, where the initial or startingpoint (z′=0) corresponds to the location of the sensor 204-1, andwherein the B_(z) or V_(H) values are shown corresponding to thelocations of the sensors 204-1, 204-2, and 204-3. In the example of FIG.4, the magnet 206 is located a distance d=30 mm from the sensor 204-1,the sensors 204-1 and 204-2 are separated by d₀=15 mm, and the sensors204-2 and 2043 are separated by d₁=15 mm. The values shown in FIG. 4 arearbitrary/illustrative, as is the units shown on each of the respectiveaxes.

In some embodiments various functions or acts may take place at a givenlocation and/or in connection with the operation of one or moreapparatuses or systems. In some embodiments, a portion of a givenfunction or act may be performed at a first device or location, and theremainder of the function or act may be performed at one or moreadditional devices or locations.

As will be appreciated by one skilled in the art, aspects of thisdisclosure may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present disclosure make take theform of an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiments combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the disclosure may take the form of a computerprogram product embodied in one or more computer readable medium(s)having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readablestorage medium. A computer readable storage medium may be, for example,but not limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific example (a non-exhaustivelist) of the computer readable storage medium would include thefollowing: an electrical connection having one or more wires, a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), an optical fiber, a portable compact disc read-onlymemory (CD-ROM), an optical storage device, a magnetic storage device,or any suitable combination of the foregoing. In the context of thisdocument, a computer readable storage medium may be any tangible mediumthat can contain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming language, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming language, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Embodiments of the disclosure may be tied to particular machines. Forexample, in some embodiments one or more devices may manage or sequencethe reading of data (e.g., voltages) from one or more sensors. Suchmanagement may include providing a value for address/select lines of amultiplexer and saving/storing one or more pieces of data (e.g., one ormore voltage readings). In some embodiments, one or more devices mayperform a computation of a distance based on the readings.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the form disclosed. Many modifications and variations will beapparent to those of ordinary skill in the art without departing fromthe scope and spirit of the disclosure. The embodiments were chosen anddescribed in order to best explain the principles of the disclosure andthe practical application, and to enable others of ordinary skill in theart to understand the disclosure for various embodiments with variousmodifications as are suited to the particular use contemplated.

The diagrams depicted herein are illustrative. There may be manyvariations to the diagram or the steps (or operations) described thereinwithout departing from the spirit of the disclosure. For instance, thesteps may be performed in a differing order or steps may be added,deleted or modified. All of these variations are considered a part ofthe disclosure.

It will be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow.

What is claimed is:
 1. A system for providing a calibration free sensor,comprising: a magnet configured to be coupled to an object under test;an array of sensors configured to measure a magnetic field associatedwith the magnet; and a circuit configured to obtain voltage readingsbased on the measured magnetic field from the array of sensors andcompute a distance between the array of sensors and the magnet based onthe obtained voltage readings.
 2. The system of claim 1, wherein themagnet comprises a spherical magnet.
 3. The system of claim 1, whereinthe array of sensors comprises at least two sensors.
 4. The system ofclaim 3, wherein the at least two sensors comprise at least two Hallsensors.
 5. The system of claim 1, wherein each sensor of the array ofsensors is configured along a line originating from the magnet.
 6. Thesystem of claim 1, wherein the circuit is configured to linearly fit theobtained voltage readings in computing the distance.
 7. The system ofclaim 1, wherein the circuit comprises a multiplexer configured toselect a voltage reading from a sensor included in the array of sensorsand a voltmeter configured to measure the selected voltage reading fromthe sensor.
 8. The system of claim 7, wherein the circuit comprises acontroller configured to provide a value for one or more address orselect lines of the multiplexer.
 9. The system of claim 8, wherein thecontroller is configured to store the obtained voltage readings from thevoltmeter in association with the value for the one or more address orselect lines.
 10. An apparatus comprising: at least one processor; andmemory having instructions stored thereon that, when executed by the atleast one processor, cause the apparatus to: obtain at least one Hallvoltage reading from each of a plurality of sensors associated with anarray of sensors, and compute a distance between a magnet coupled to anobject under test and the array of sensors based at least in part on theobtained Hall voltage readings.
 11. The apparatus of claim 10, whereinthe instructions, when executed by the at least one processor, cause theapparatus to: compute the distance between the magnet coupled to theobject under test and the array of sensors based at least in part on oneor more predetermined separations between the plurality of sensors. 12.The apparatus of claim 10, wherein the instructions, when executed bythe at least one processor, cause the apparatus to: sequence througheach sensor of the plurality of sensors in obtaining the at least oneHall voltage reading from each of the plurality of sensors, and save theobtained at least one Hall voltage reading from each of the plurality ofsensors in association with indicia indicative of a selected sensor inthe sequence.
 13. The apparatus of claim 10, wherein the instructions,when executed by the at least one processor, cause the apparatus to:linearly fit the obtained Hall voltage readings in computing thedistance.
 14. The apparatus of claim 10, wherein the instructions, whenexecuted by the at least one processor, cause the apparatus to: obtain aplurality of Hall voltage readings from each of the plurality ofsensors, and filter the Hall voltage readings from each sensor to obtaina final Hall voltage reading for each sensor in computing the distance.15. The apparatus of claim 14, wherein the final Hall voltage readingfor each sensor comprises an average of the plurality of Hall voltagereadings from the sensor.